Tower for a Wind Turbine, Prefabricated Metal Wall Part for Use in a Tower for a Wind Turbine and Method for Constructing a Tower for a Wind Turbine

ABSTRACT

A tower for a wind turbine. The tower has an exterior side and an interior side. The tower is at least partly composed of prefabricated metal wall parts. Each wall part includes an essentially quadrangular portion having an outwardly facing surface in the direction of the exterior of the tower and an inwardly facing surface in the direction of the interior of the tower. The portion having a top edge, a bottom edge, a first side edge and a second side edge. The first side edge is provided with a first flange along at least part of the length of the first side edge and the second side edge is provided with a second flange along at least part of the length of the second side edge. A method for constructing a tower for a wind turbine.

This invention relates to a tower for a wind turbine which has anexterior side and an interior side and which tower is at least partlycomposed of prefabricated metal wall parts. The invention also relatesto a prefabricated metal wall part for use in a tower for a windturbine. The invention further relates to a method for constructing atower for a wind turbine which has an exterior side and an interior sideand wherein the tower is at least partly composed of prefabricated metalwall parts.

An ongoing trend in the wind turbine market is the increasing power ofthe wind turbine in conjunction with increasing tower heights. Largerwind turbines imply an increase in size, weight and loads acting on thetower of the wind turbine. This requires the towers to be stronger andstiffer, and consequently lead to bigger tower dimensions.

Conventional tubular steel towers for wind turbines of 2 MW and aboverequire very large tower diameters and/or large wall thickness to takethe large static and fatigue loads which are exerted on the windturbine. These large towers are usually constructed by prefabricating anumber of tower sections from metal plate by welding curved platestogether, often referred to as “cans”, and transporting these sectionsto the site where the tower is to be erected. These sections or cans arebolted to the foundation of the tower and to each other using curvedL-type flanges requiring a large number of large bolts. The increasingpower of the wind turbines also require the flanges to be produced withan increasing accuracy as to flatness. For land transport, the diameterof the tower section is the main restriction. A diameter of about 4.3 mis usually the upper limit that can be transported to most locations inview of fly-overs etc., and the weight of the section imposes its limitsas well.

In use, the forces exerted on the top of the tower by the rotor-turbineassembly determine the load, i.e. the bending moments at all essentiallyhorizontal flange connections and welds. The ultimate strength isdetermined by the yield strength of the bolts and by the bucklingstrength of the tubular metal wall. For the fatigue strength the weldsare critical. During service, it is very difficult to inspect thequality of a weld. Also, on-site repairs are awkward.

Apart from the strength, the dynamic behaviour of the tower is anotherdetermining factor. The turbine would be severely damaged if it were tooperate at its natural resonance frequency. CONFIRMATION COPY

It is known to increase natural frequency and/or the strength and/orstiffness of a wind turbine by increasing the thickness of the metalplate and/or the diameter of the tower. However, transport problems dueto size and weight of the tower sections make this solution impractical.Also lattice towers have been used to increase the stiffness of towersfor wind turbines. However, lattice towers require a very large number(>2000) of individual parts, significant amounts of maintenance and areconsidered visually unattractive. Moreover, the dynamic behaviour ofsuch towers is not adequate for large towers. Guyed towers have alsobeen used for wind turbines. These towers are guyed with steel cables atabout half the height of the tower. Obviously, this poses a designproblem as the cables may not come into contact with the rotor of thewind turbine. Moreover, the costs of the foundations for the cables andthe cables itself (with diameters of about 100 mm) are high. Also thecables need to have high fatigue strength.

Hybrid towers, such as towers with concrete walls, poured between aninner and outer steel shell have also been proposed. The problem is toassure the quality of the wall, once it has been poured. Whenconstructing a tower for a wind turbine using prefabricated concreteelements, tension means are required to keep the concrete wall undercompressive forces. Moreover, concrete towers are not an economicalsolution.

It is the object of this invention to provide a tower for a wind turbinewhich provides a large stiffness. It is another object of this inventionto provide a tower for a wind turbine which provides sufficient strengthto enable application of high power generators on top of the tower. Itis still another object of this invention to provide a tower for a windturbine which does not cause the aforementioned transport problems, evenfor very large towers and/or towers with a wide base.

According to a first aspect of the invention, one or more of theseobjects can be reached by a tower for a wind turbine wherein the towerhas an exterior side and an interior side and wherein the tower is atleast partly composed of prefabricated metal wall parts wherein eachwall part comprises an essentially quadrangular portion having anoutwardly facing surface in the direction of the exterior of the towerand an inwardly facing surface in the direction of the interior of thetower, said portion having a top edge, a bottom edge, a first side edgeand a second side edge, wherein the first side edge is provided with afirst flange along at least part of the length of the first side edgeand wherein the second side edge is provided with a second flange alongat least part of the length of the second side edge. By using theprefabricated metal wall parts according to the invention, the stiffnessof the construction is increased by the presence of the flanges of theprefabricated metal wall parts, which act as a rib. By usingprefabricated metal wall parts, the transport of complete tower sectionsis no longer required, thus solving the transport problem. Theprefabricated metal wall parts are easy to transport with ordinarytransport means such as trucks. Also, by using the prefabricated parts,the size of the tower at the foundation is no longer limited by thetransport restrictions and a wider base can be used. It also allowsconstruction of higher towers because the size of the base is no longeran issue. The wider base results in a lower local pressure on thefoundation, thus enabling to use a simpler foundation. The wider basealso contributes to the stiffness of the tower, thereby enabling to usehigh power generators on top of the tower. In an embodiment of theinvention the tower is substantially composed of prefabricated metalwall parts. The tower according to this embodiment relies onprefabricated metal wall parts as the load bearing elements, and arereadily distinguishable from concrete towers, where a wall part servesas a mould for the concrete to be poured in and where, after setting,the concrete serves as the main load bearing material. It should benoted that the tower according to the invention does not compriseconcrete as a load bearing material at the location of the prefabricatedmetal wall parts. It should also be noted that it is possible toconstruct a tower according to the invention on top of a concretefoundation or base wherein the concrete base extends upwardly, the baseforming the lower part of the tower, and a tower according to theinvention forming the upper part of the tower.

In an embodiment of the invention the first flanges and the secondflanges of the prefabricated metal wall parts extend towards theinterior side of the tower This enables to produce a tower where therib, formed by the adjacent flanges, is located on the inside of thetower, leaving a smooth exterior appearance. A smooth exterior leads toa reduced impact of wind force on the tower and a smooth exterior isconsidered to be visually more attractive.

In an embodiment of the invention, the prefabricated metal wall partshaving a height and a width, at least two of the prefabricated metalwall parts have a height which is about 2.5 times larger than the widthof the bottom edge, preferably more than five times larger, morepreferably more than 10 times larger. It should be noted that the heightof the prefabricated metal wall parts is to be understood to be thedistance between the bottom edge and the top edge of the prefabricatedmetal wall parts when present in the tower. It should be understood thatthe length direction is defined in the direction of the height of thetower. This means that the tower comprises prefabricated metal wallparts which are considerably higher than wide, thus resulting in longside edges of the essentially quadrangular portion of the prefabricatedmetal wall parts and thereby enabling long flanges being provided atleast partly on the side edge thereof. These long flanges enable a largestiffening potential of the tower.

In an embodiment of the invention the first flange of a prefabricatedmetal wall part is attached to the second flange of an adjacent secondprefabricated metal wall part by fastening means. The flanges are nowfixedly connected, thereby increasing the stiffening potential becauseof the double thickness of the rib. Fastening means comprise forinstance a weld or a rivet. In a preferred embodiment of the invention,the fastening means comprise nuts and bolts. This enables to fastenquickly the first and second flange of two adjacent panels to eachother. The holes required for the bolts to be inserted into may alreadybe present in the prefabricated metal wall parts or may be drilled atthe site where the connection between the adjacent panels is made. Theuse of nuts and bolts also enables to temporarily undo the connection,for instance to remove a prefabricated metal wall part from theconstruction, or to replace a prefabricated metal wall part. It alsoallows easy on-site and/or off-site inspection.

In an embodiment of the invention the essentially quadrangular portionof the prefabricated metal wall parts is preferably orthogonal ortrapezial wherein the length of the first side edge is approximatelyequal to the length of the second side edge and wherein the bottom edgeis longer than the top edge. In case of constructing an essentiallycylindrical tower, the use of orthogonal prefabricated metal wall partsis called for, in case of constructing a conical tower, trapezialprefabricated metal wall parts are called for. Conical towers enable toconstruct a tower with a large base and become slimmer with increasingheight of the tower. Tapering can be over the entire height of the toweror over part of the length of the tower. The latter can also be achievedby using prefabricated metal wall parts to form essentially cylindricaltower sections and by using prefabricated metal wall parts to formessentially conical tower sections and combine these tower sections intoone tower.

Kinked prefabricated metal wall parts may be used in the upper levels ofa conically tapered tower or tower section for a wind turbine whereinthe lower levels are made using prefabricated metal wall parts with anessentially flat quadrangular portion, thus reducing the number ofprefabricated metal wall parts required for a full ring. Oneprefabricated metal wall part with one kink in the essentiallyquadrangular portion in a given upper level ring will link up with twoprefabricated metal wall parts which have an essentially flatquadrangular portion in the ring immediately below the upper level ring.In case the kinked prefabricated metal wall parts contains more kinks,it may link up with a corresponding number of prefabricated metal wallparts with an essentially flat quadrangular portion. It will be clearthat kinked prefabricated metal wall parts in a lower level can also becombined with kinked prefabricated metal wall parts in the upper level.

In an embodiment of the invention the tower has an essentially annular,preferably essentially circular horizontal cross-section. An essentiallyannular horizontal cross section is also obtained if a polygonalhorizontal cross section is taken with a large number of facets such asa pentagon or hexagon.

In an embodiment of the invention the essentially quadrangular portionof the prefabricated metal wall parts are curved with a radiuscorresponding to the radius of the tower at the position of the locationof the prefabricated metal wall part. This allows constructing a towerwith a smooth curvature, and in case the first and second flanges extendtowards the interior side of the tower, the exterior of the tower willbe smooth. In another embodiment of the invention the quadrangularportion of the first prefabricated metal wall parts is essentially flat.The use of an essentially flat quadrangular portion has the advantagethat there is no need for a locally dependent curvature in thequadrangular portion and is therefore easier to produce. It is also moreconvenient during transport of the prefabricated metal wall parts. Theapplication of such prefabricated metal wall parts causes the exteriorof the tower to be polygonal. In still another embodiment theessentially flat quadrangular prefabricated metal wall parts alsocomprises at least one kink essentially in the direction between thebottom edge and the top edge of the prefabricated metal wall part. Thekink (or kinks) therefore runs in the direction of the height of thetower. With the kink (or kinks) a higher buckling stiffness of theprefabricated metal wall part is obtained. It may also increases thenumber of facets of the polygonal thereby achieving a smoother exteriorof the tower.

The invention is also embodied in a tower for a wind turbine asdescribed hereinabove wherein the first flange is provided with anadditional first flange along at least part of the length of the firstflange and/or wherein the second flange is provided with an additionalsecond flange along at least part of the length of the second flange.This is advantageous for instance for a further increase in stiffeningthe tower, particularly when the first flange and second flange are bothprovided with an additional flange, wherein the first flange with itsrespective additional flange preferably essentially forms an L-shapeand/or wherein the second flange with its respective additional flangepreferably essentially forms an L-shape. For the purpose of thisapplication, these additional flanges on the first and/or second flangesmay be used to attach objects thereto such as stairs, or internalfloors.

The invention is also embodied in a tower for a wind turbine asdescribed hereinabove wherein the first and/or second flanges are atleast partly folded back towards the inwardly facing surface of theessentially quadrangular portion of the prefabricated metal wall part,thereby effectively doubling the thickness of the flanges. This doublingof the flanges causes an additional stiffening of the construction. Itwill be clear to the skilled person that the flange could also be foldedback twice or more contributing to the stiffening effect.

In an embodiment of the invention the prefabricated metal wall parts aresteel parts, preferably high strength steel parts, for instance having ayield strength of about 355 MPa or higher. The use of steel enables touse prefabricated metal wall parts of a small thickness, which reducesthe weight of the tower. The use of high strength steel prefabricatedmetal wall parts enables a further reduction in weight of the tower. Asa result, the foundation of the tower can be constructed more efficient.

In an embodiment of the invention the first flange of a firstprefabricated metal wall part is vertically staggeredly attached to thesecond flange of an adjacent second prefabricated metal wall part byfastening means. This application of prefabricated metal wall parts by astretching bond type connection of the flanges of two adjacentprefabricated metal wall parts also requires the application ofprefabricated metal wall parts of different lengths, at least in thefirst and last ring of the tower or tower section. The application ofthis staggered connection has the advantage over constructing the towerfrom rings of connected non-staggeredly connected prefabricated metalwall parts that the forces are lead through the construction withouthaving to be led through horizontal flanges which connect theaforementioned rings. The overlap at the edges between the staggeredlyconnected prefabricated metal wall parts is between 1:2 and 1:4,preferably about 1:3, meaning that about ½ to ¾, preferably about ⅔ ofthe respective side edges of adjacent prefabricated metal wall partsoverlap.

In another embodiment of the invention the circumference of the towerconsists of n adjacently positioned prefabricated metal wall parts,wherein the angle between the first flange and the second flange is360/n.

According to a second aspect of the invention, the prefabricated metalwall part for use in a tower for a wind turbine as described hereinaboveis characterised in that the prefabricated metal wall part comprises anessentially quadrangular portion having an outwardly facing surface andan inwardly facing surface, said portion having a top edge, a bottomedge, a first side edge and a second side edge, wherein the first sideedge is provided with a first flange along at least part of the lengthof the first side edge and wherein the second side edge is provided witha second flange along at least part of the length of the second sideedge.

According to a third aspect of the invention, a method is provided forconstructing a tower for a wind turbine as described hereinabove,wherein the tower is at least partly composed of prefabricated metalwall parts as described hereinabove.

When constructing a tower according to the invention, there is no needfor a high capacity crane to lift the tower sections on top of eachother at the site where the tower is constructed. A relatively smallbuilding crane will be adequate to lift one prefabricated metal wallparts at a time, except in the case tower complete tower sections arebuilt from the prefabricated metal wall parts which are then hoistedupon the foundation or the tower section already present. In that case amore powerful crane is required.

The absence of horizontal welds in the towers according to the inventioneliminates a known source of fatigue failure, thereby allowing torelieve design restrictions for instance by allowing to use thinnergauge metal plate. The locations where a bottom edge of a firstprefabricated metal wall part touches a top edge of a prefabricatedmetal wall part which is located immediately below the firstprefabricated metal wall part can be sealed by using sealing means, forinstance a sealant. This prevents the outside atmosphere to enter thestructure and prevents corrosion. The locations where the first flangeof a prefabricated metal wall part is connected to the second flange ofthe adjacent prefabricated metal wall part can, if so desired, also besealed using sealing means, such as a sealant.

In an embodiment of the invention the tower is provided with stiffeningmeans, such as one or more preferably substantially horizontalstiffening rings. These stiffening means are preferably provided in theinterior of the tower to absorb the horizontal forces exerted on thetower. These stiffening means may be provided at different heights ofthe tower. The prefabricated metal wall parts are connected to the ring,thereby obtaining an increased stiffness of the tower. Additionalconnecting struts may be used to connect the prefabricated metal wallparts to the ring. The stiffening means may also be formed by internalfloors, or the stiffening means, such as a stiffening ring alonginternal circumference of the tower, may provide the base for theinternal floor or floors. The stiffening means may also contribute tothe even distribution of forces and loads over the entire circumferenceof the tower.

The prefabricated metal wall parts can be produced for example fromhot-rolled metal using commonly known technology. The hot-rolled metalmay be plate material or coiled material. This material, after optionalleveling can be cut to the desired dimensions and shape, and the flangescan be formed on the edges of the essentially quadrangular portion ofthe prefabricated metal wall parts using conventional bendingtechniques. The optional curvature of the essentially quadrangularportion of the prefabricated metal wall parts or the kink or kinks canlikewise be easily introduced. The prefabricated metal wall parts may becoated prior to use in the tower e.g. with zinc and/or an organiccoating to extend the service life and to reduce maintenance.

The prefabricated metal wall parts may also comprise additional built-infunctionality such as a door for entering the interior of the tower.Internal structures like stairs and floors can be easily installed.

The present invention will now be further explained by the followingnon-limitative drawings and examples.

In these drawings:

FIG. 1 is a schematic representation of a wind turbine;

FIG. 2 is a schematic representation of a tower for a wind turbineaccording to the state of the art (not to scale);

FIG. 3 is a schematic representation of towers for a wind turbineaccording to the invention (not to scale);

FIG. 4 is a schematic representation of a prefabricated metal wall partsaccording to the invention (not to scale);

FIG. 5 is a schematic cross-section of the first ring of a tower for awind turbine also highlighting a schematic representation of the boltedconnection;

FIG. 6 is a schematic representation of an L-shaped flange.

FIG. 7 is a schematic representation of the tower construction at thelocation of a stiffening ring.

In FIG. 1 a schematic representation of a wind turbine 1 is shown. Thewind turbine 1 comprises a generator 2, a rotor 3 and a tower 4 ontowhich the combination of the generator and the rotor is mounted. Thetower 4 has an exterior surface which forms the outside of the tower 4and an interior surface which forms the inside of the tower. The towerconsists of four tower sections 4 a-4 d. The wind turbine is placed on afoundation 19.

In FIG. 2 a tower 4 for a wind turbine according to the state of the artis shown. Tower segments 4 a, 4 b, 4 c and 4 d are mounted on top ofeach other. These tower segments are made off-site and connected throughhorizontal flanges and large bolts and nuts. These flanges are indicatedschematically by the thick horizontal lines between the tower sections.The tower segments are made from curved plates which are welded togetherhorizontally and vertically. These welds, indicated with the dashedlines, are known to be a possible source of fatigue failure,particularly the horizontal welds. For a tower of about 80 m high, abase of about 4.3 m and a top diameter of about 2.3 m is commonly used.The dimension of the base is limited by transport limitations.

In FIG. 3 a a tower 4 for a wind turbine according to the invention isshown, wherein the staggered prefabricated metal wall parts each staggerover about half the length of the neighbouring prefabricated metal wallpart and FIG. 3 b shows a tower wherein the staggered prefabricatedmetal wall parts each stagger over about a third of the length of theneighbouring prefabricated metal wall part. The base of the tower isabout 6.5 m in diameter whereas the top of the tower has a diameter ofabout 2.3 m. The 6.5 m base diameter poses no transport problems becauseit can be transported to the building site in pieces. The increase inwidth of the base of the tower increases the stiffness of the tower. Italso enables to construct higher towers width adequate stiffness toinstall high power wind turbines.

FIG. 4 a shows an embodiment of a prefabricated metal wall part 5according to the invention for use in a tower 4 for a wind turbine 1 asdescribed hereinabove. The prefabricated metal wall part 5 ischaracterised in that the wall part comprises an essentiallyquadrangular portion 6 having an outwardly facing surface 7 facing theexterior of the tower and an inwardly facing surface 8 facing theinterior of the tower, said portion having a top edge 9, a bottom edge10, a first side edge 11 and a second side edge 12, wherein the firstside edge 11 is provided with a first flange 13 along at least part ofthe length of the first side edge 11 and wherein the second side edge 12is provided with a second flange 14 along at least part of the length ofthe second side edge 12. The first flange 13 is provided with anadditional first flange 15 which essentially forms an L-shape with thefirst flange 13 and the second flange 14 is provided with an additionalsecond flange 16 which essentially forms an L-shape with the secondflange 14. The prefabricated metal wall parts are not drawn to scale.The cross section A-A is shown in FIG. 4 b. Typical dimensions for sucha prefabricated metal wall parts for the lower ring of a conical toweror tower segment would be a width at the top edge 9 of between about0.60 and 1.00 m, for example about 0.86 m, a width at the bottom edge 10of between about 1.30 and 0.70 m, for example about 1.04 m, a height ofbetween about 10 and 20 meters, for example 20 meters, and a height ofthe extending first flange 13 and second flange 14 of between 0.10 and0.20 m, for example about 0.15 m. A typical thickness of theprefabricated metal wall parts would be between 8 and 16 mm, for exampleabout 12 mm.

In FIG. 5 a a schematic cross section of the first ring of a tower for awind turbine is shown. The essentially circular cross-section of thetower in this example is composed of eighteen prefabricated metal wallparts 5. The exterior of the tower is indicated by 4′, the interior ofthe tower is indicated by 4″. In this embodiment of the invention, thefirst flange of each prefabricated metal wall parts is attached to thesecond flange of the adjacent prefabricated metal wall parts by boltsand nuts which are passed through holes in the first and second flange.FIG. 5 b shows a part of the first ring with the prefabricated metalwall parts 5 and the nuts and bolts 17.

In FIG. 6 a schematic representation is shown of the L-shaped flange 18which can be used to attach prefabricated metal wall parts of the firstring to the foundation 19 of the tower, or to the top ring on which thegenerator is attached.

In FIG. 7 a schematic representation of part of the tower constructionat the location of a stiffening ring is shown. The adjacent, staggeredlyconnected prefabricated metal wall parts are connected using an overlapat the edges (i.e. in a stretcher-bond type connection) of 1:3 and arealso connected to the stiffening ring 20 using connecting struts 21. Asshown, these connecting struts 21 are connected to the flanges 13, 14(see FIG. 4) of the prefabricated metal wall parts on one side, and tothe stiffening ring 20 on the other side. In FIG. 7 four prefabricatedmetal wall parts are shown which are indicated with A, B, C and D. Thelower edge of part A and the upper edge of part B are adjacent. Thefirst side edge of part A is adjacent and connected to the second sideedge of part C by their adjacent flanges and fastening means (notshown). The connecting struts 21 extend above and below the stiffeningring 20, thereby enabling fixedly connecting the side edges of upper part A to the side edges of lower part B. Due to the 1:3 overlap in thisexample only about ⅓ of the circumference of the tower has a horizontalseam at or near the location of the stiffening ring. In the example ofFIG. 8 the horizontal seam between part A and B is located near thestiffening ring 20.

To construct a tower for a wind turbine according to the invention it ispossible to first form a full ring of the tower by attaching at leasttwo adjacent prefabricated metal wall parts along their adjacentflanges. This first full ring can be connected to an essentially flatand essentially horizontal foundation for the tower. Of course, the sameresult is obtained when starting with a first prefabricated metal wallpart which is attached to the foundation after which a secondprefabricated metal wall part is attached to the first prefabricatedmetal wall part and the foundation. Similarly, the following full ringcan be constructed upon the ring already present by first building theentire ring and subsequently lifting is on top of the ring alreadypresent, or by connecting prefabricated metal wall parts to the ringalready present and to each other one by one, the former procedurerequiring a larger capacity crane than the latter procedure. Rings areadded to the rings already present until the desired height of the toweris obtained.

The connection between the first full ring and the foundation may beachieved by using a flange that is connected to the foundation. In caseof using prefabricated metal wall parts with an essentially flat orkinked quadrangular portion, the flanges may be simple L-shaped flanges.In case of using prefabricated metal wall parts with a curvedquadrangular portion, the flanges should have a corresponding curvature.

To construct a tower for a wind turbine according to the invention it ispossible to first form a full ring of the tower by attaching at leasttwo adjacent prefabricated metal wall parts along their adjacent flangesvertically staggeredly. This implies the use of prefabricated metal wallparts of different lengths. In the example of FIG. 3 a, full lengthprefabricated metal wall parts are combined with prefabricated metalwall parts of half that length whereas in the example of FIG. 3 b, fulllength prefabricated metal wall parts are combined with prefabricatedmetal wall parts of ⅔ and ⅓ of that length (i.e. an overlap of 1:3). Offcourse, it is also possible to stagger the prefabricated metal wallparts differently than those mentioned in FIG. 3. These embodiments arealso considered to be part of the invention. After the first full ringhas been completed and connected to the foundation, the remainder of thetower is constructed using essentially full length prefabricated metalwall parts. In the last full ring prefabricated metal wall parts ofdifferent lengths have to be used to make the top edge of the last ringlevel. Of course it is also possible to use prefabricated metal wallparts of non-full length elsewhere in the tower if so desired. Thisstaggeredly attaching the prefabricated metal wall parts provides in alarge stiffness of the tower, without introducing horizontal fullyannular or circular flanges to connect tower sections.

When constructing a tower according to the invention, the tower may beconstructed top down by starting to construct the top of the towerwhilst being suspended onto a yoke construction, the yoke constructionbeing provided with lifting means, such as a hydraulic jack. By firstcompleting a full ring of the tower, preferably by connecting theprefabricated metal wall parts staggeredly, only just above groundlevel, and subsequently lifting the ring using the yoke and jacks, thefollowing parts can also be mounted just above ground level. This way,there is no need for very high cranes during the construction of thetower, and the construction can be largely performed just above groundlevel, where wind forces are usually more moderate than high in the air.Also, correction of any misalignment is easier to perform. Anotheradvantage of this top-down or push-up method is that it is morepractical to fit a stiffening ring from below in a tapered constructionand simultaneously using it to align the prefabricated metal wall partsand to optionally correct any misalignment.

It is of course to be understood that the present invention is not inany way limited to the described embodiments and examples describedabove, but encompasses any and all embodiments within the scope of thedescription and the following claims.

1. Tower for a wind turbine having an exterior side and an interiorsides, the tower at least partly comprising prefabricated metal wallparts, wherein each wall part comprises an essentially quadrangularportion having an outwardly facing surface in the direction of theexterior of the tower and an inwardly facing surface in the direction ofthe interior of the tower, said portion having a top edge, a bottomedge, a first side edge and a second side edge, wherein the first sideedge is provided with a first flange along at least part of the lengthof the first side edges, and wherein the second side edge is providedwith a second flange along at least part of the length of the secondside edge.
 2. Tower for the wind turbine according to claim 1, whereinthe first flanges and the second flanges of the prefabricated metal wallparts extend towards the interior side of the tower.
 3. Tower for thewind turbine according to claim wherein each of the prefabricated metalwall parts have a height and a width, and wherein at least two of theprefabricated metal wall parts have a height which is at least about 2.5times larger than the width of the bottom edge.
 4. Tower for the windturbine according to claim 1, wherein the first flange of a saidprefabricated metal wall part is attached to the second flange of anadjacent said prefabricated metal wall part by fastening means.
 5. Towerfor the wind turbine according to claim 1, wherein the essentiallyquadrangular portion of the prefabricated metal wall parts isessentially rectangular wherein the length of the first side edge isapproximately equal to the length of the second side edge and whereinthe bottom edge is approximately equal to the length of the top edge, orwherein the essentially quadrangular portion of the prefabricated metalwall parts is essentially trapezial wherein the length of the first sideedge is approximately equal to the length of the second side edge andwherein the bottom edge is longer than the top edge.
 6. Tower for thewind turbine according to claim 1 wherein the tower has an essentiallyannular, horizontal cross-section.
 7. Tower for the wind turbineaccording to claim 1, wherein the essentially quadrangular portion ofthe respective prefabricated metal wall parts are curved.
 8. Tower forthe wind turbine according to claim 1, wherein the essentiallyquadrangular portion of the respective prefabricated metal wall part isessentially flat.
 9. Tower for the wind turbine according to claim 1,wherein the first flange is provided with an additional first flangeand/or wherein the second flange is provided with an additional secondflange.
 10. Tower for the wind turbine according to claim 1, wherein thefirst flanges and/or the second flanges are at least partly folded backtowards the inwardly facing surface of the essentially quadrangularportion of the prefabricated metal wall part for at least partlydoubling the thickness of the first flanges and/or second flanges. 11.Tower for the wind turbine according to claim 1, wherein theprefabricated metal wall parts are steel parts.
 12. Tower for the windturbine according to claim 1, wherein the first flange of at least onesaid prefabricated metal wall part is vertically staggeredly attached tothe second flange of an adjacent said prefabricated metal wall part byfastening means.
 13. Tower for the wind turbine according to claim 1,wherein the circumference of the tower consists of n adjacentlypositioned prefabricated metal wall parts, wherein the angle between thefirst flange and the second flange is 360/n.
 14. Tower for the windturbine according to claim 1, wherein the tower is provided withstiffening means.
 15. Prefabricated metal wall parts for use in a towerfor a wind turbine at least partly composed of a plurality of saidprefabricated metal wall parts, comprising: an essentially quadrangularportion having an outwardly facing surface and an inwardly facingsurface, said portion having a top edge, a bottom edge, a first sideedge and a second side edge, wherein the first side edge is providedwith a first flange along at least part of the length of the first sideedge, and wherein the second side edge is provided with a second flangealong at least part of the length of the second side edge.
 16. Methodfor constructing a tower for a wind turbine according to claim 1 atleast partly composed of said prefabricated metal wall parts, comprisingattaching one said prefabricated metal wall part to an adjacent saidprefabricated wall part.
 17. Tower for the wind turbine according toclaim 1, wherein each of the prefabricated metal wall parts have aheight and a width, and wherein at least two of the prefabricated metalwall parts have a height which is more than five times larger than thewidth of the bottom edge.
 18. Tower for the wind turbine according toclaim 1, wherein each of the prefabricated metal wall parts have aheight and a width, and wherein at least two of the prefabricated metalwall parts have a height which is more than ten times larger than thewidth of the bottom edge.
 19. Tower for the wind turbine according toclaim 1, wherein the first flange of a said prefabricated metal wallpart is attached to the second flange of an said adjacent prefabricatedmetal wall part by fastening means comprising nuts and bolts.
 20. Towerfor the wind turbine according to claim 1, wherein the tower has anessentially circular horizontal cross-section.
 21. Tower for the windturbine according to claim 1, wherein the essentially quadrangularportion of the respective prefabricated metal wall part is essentiallyflat, and wherein the essentially quadrangular portion of the respectiveprefabricated metal wall part also comprises at least one kinkessentially in the direction between the bottom edge and the top edge ofthe prefabricated metal wall part.
 22. Tower for the wind turbineaccording to claim 1, wherein the prefabricated metal wall parts arehigh strength steel parts.
 23. Tower for the wind turbine according toclaim 1, wherein the first flange of at least one said prefabricatedmetal wall part is vertically staggeredly attached to the second flangeof an adjacent said prefabricated metal wall part by fastening means,wherein more than half of the adjacently positioned prefabricated metalwall parts are attached vertically staggeredly.
 24. Tower for the windturbine according to claim 1, wherein the tower is provided withstiffening means comprising one or more stiffening rings.
 25. Tower forthe wind turbine according to claim 1, wherein the tower is providedwith stiffening means comprising one or more substantially horizontalstiffening rings.